1. Field of the Invention
The present invention is concerned with a process for treating wastewater containing volatile compounds to degrade the volatile compounds without liberating them to the atmosphere.
2. Information Disclosure Statement
Aerobic biological treatment of wastewaters which contain volatile compounds can result in the emission of the volatile compounds into the environment. The volatile compounds are stripped from the aqueous phase during the process of transferring oxygen to the wastewater. Whether the aeration is accomplished by bubble or surface aeration makes little difference in the volatilization affect.
Studies by Weber and Jones, "Toxic Substance Removal in Activated Sludge and PAC Treatment Systems", EPA/600/S2-86/045, June, 1986 demonstrated that addition of powdered activated carbon to an aerobic biological system results in greatly reduced stripping of volatile compounds.
The addition of powdered adsorbent to the activated sludge process aeration basin constitutes the Powdered Activated Carbon Treatment (PACT.RTM.) process. Examples of such process are described in U.S. Pat. Nos. 3,904,518 and 4,069,148. The preferred powdered adsorbent is powdered activated carbon.
Meidl in U.S. Pat. No. 4,857,198 discloses treating a wastewater containing volatile compounds by air stripping the water to drive the compounds into the gas phase, then capturing the volatile compounds by contacting the stripping air with an aqueous mixture of biological solids and powdered adsorbent. The stripped wastewater is further treated by a biophysical aerobic process which in turn produces the biological solids and powdered adsorbent used to trap the volatile compounds.
Cournoyer et al. in U.S. Pat. No. 4,894,162 and No. 5,106,496 disclose a process and apparatus for purifying waste gases containing volatile compounds emanating from waste liquids by enclosing all tanks and basins from the influent of the wastewater treatment plant up to the aeration treatment zone and venting these gases to an aerobic digester and/or an aeration basin to biologically decompose or degrade the volatile compounds. The tank enclosures and extra piping are a significant additional expense.
The aeration of return sludge from a clarifier to an aeration zone in a biological treatment process has been described by Reimann in U.S. Pat. No. 3,953,326; by Hell et al. in U.S. Pat. No. 4,629,565; and by Bogusch in U.S. Pat. No. 4,705,633.
Applicant has discovered a process which overcomes the need for many of these added treatment steps and results in the biological decomposition or degradation of volatile compounds in wastewaters before treatment in an aerobic biophysical process. Governmental regulations may require covering the aeration zone of an aerobic treatment process to prevent escape of volatile compounds to the atmosphere, as well as treatment of the contained gases to remove volatile compounds. Applicant's invention removes the volatile compounds from the wastewater prior to aeration, thus overcoming the necessity to capture and treat aeration zone offgases resulting in significant savings in wastewater treatment costs.